The action of the human heart is controlled by propagation of electrical activity in various regions of the heart. The presence of abnormal accessory pathways in the heart can lead to conditions such as ventricular tachycardia and atrial flutter.
Physicians have found that they can detect malfunctions of the heart by probing the heart with a catheter fitted with one or more electrodes and having steering capability, measuring voltages within the heart, and observing the waveforms. Once a physician understands how the electrical activity of the heart is operating he can, if he wishes to do so, choose to “disconnect” certain portions of the heart electrically by the process of ablation.
The electrical activity of the heart is detected and read in accordance with a mapping procedure to determine the presence of abnormal accessory pathways in the heart. A typical mapping procedure involves using electrophysiology sensing electrodes mounted on a catheter as remote controlled voltage testing probes to test various locations in the heart. This mapping is known as electrophysiology (EP) testing and can be used to diagnose sinus node dysfunction, identify arrhythmias, check impulse generation or conduction in the atria and ventricles, or investigate the need for pacemakers or implantable cardiac defibrillator.
Ablation is sometimes performed as a part of the EP test to destroy small amounts of heart tissue that are interfering with electrical impulses, or causing arrhythmias. The process of ablation is a destructive process in which a portion of a catheter (typically the tip) is used to apply a short burst of RF energy to the heart tissue to burn a certain section of the heart, which stops the propagation of an electrical signal from one portion of the heart to another.
Existing EP catheters are typically positioned at various positions in the heart under fluoroscopic guidance. The x-rays show the catheter, and can also show the heart itself and thus the position of the catheter relative to the heart (if dye injections are made). The clinician tries to visualize the position of the catheter in the heart in the various chambers. Electrical means are used to determine whether or not the electrode is in contact with the heart, and this information is collected in a computer and/or shown on an EKG display. During the course of a typical procedure the operator will frequently return to one or more positions, and will look for particular waveforms that he sees from the sensing electrodes to determine whether the catheter has returned to the desired position. Particular methods of mapping include activation sequence mapping, voltage amplitude mapping, pacing morphology mapping, and entrainment mapping. Typically, more than one catheter is used in a given procedure, and the catheters are constructed with steering or torquing devices that assist in positioning of the catheters within the heart.
Unfortunately, the use of fluoroscopy for ascertaining the catheter position does not provide adequate detail in real time and also exposes the patient and health professionals to undesirable ionizing radiation. Other visualization technologies, such as electromagnetic mapping of the catheter location, are expensive and also lack desirable accuracy.
The present application is directed to the use of high frequency ultrasound visualization during EP procedures and provides, in one particular form, a novel catheter for use in EP procedures which can produce high resolution, real time ultrasound images that are coincident with the location of the electrodes so as to provide unambiguous visual feedback to the operator. Novel catheter designs and methods of construction are also disclosed for producing ultrasound imaging catheters for these and other diagnostic and/or therapeutic applications.